Distraction and Preoccupation
Being distracted or preoccupied may usurp the limited capacity of the conscious mind to the point we are unaware of our surroundings. Distraction occurs when our mental focus is preoccupied with some external stimulus, such as searching for car keys in a purse. Preoccupation occurs when our mental focus dwells on some internal stimuli, such as worrying or daydreaming.
Distraction and preoccupation are inevitable. However, if they occur when you should be attending to your surroundings, you may be unaware of a danger. You must be aware of times when a higher level of vigilance is necessary and minimize distraction and preoccupation during those times.
Imagine that your attention is a beam of light. Whatever you point the beam at, you notice, while the surrounding area is not noticed. We must learn to beam our attention at details relevant to our safety.